Igniting and sensing flame on a fuel gas burner

The present invention relates to the ignition of a fuel gas-air mixture on a burner, such as used in an oven and has particular applicability to igniting such a mixture in an oven used for household cooking, particularly of the type produced in high volume for residential kitchens. Heretofore, ignition of fuel gas-air mixture in oven burners has been performed generally in one of two ways: (a) providing a glowing hot surface igniton adjacent the burner port and permitting the fuel gas-air mixture to impinge upon the glowing surface of the ignitor to be raised to ignition temperature to ignite the flame, (b) providing a high voltage spark discharge in the path of the fuel gas-air mixture flowing from the burner port. The spark discharge manner of igniting fuel gas-air mixture has found widespread usage because of the relatively low manufacturing cost and ease of assembly of the components in the oven and the minimum of space required for such a spark discharge ignitor in the region surrounding the burner.

However, problems have been encountered in igniting a fuel gas-air mixture flowing from a burner port with a spark ignitor because of the relatively high velocity of the mixture discharging from the burner port and from spark erosion of single point electrode sparking. Problems have also been encountered with alignment of the electrodes both during manufacture and in maintaining alignment during service life resulting erratic sparking and unreliable ignition. The flame generating ports must be maintained to a minimal size to prevent generation of oversized flames which are difficult to control and which have a tendency to burn rich resulting in hydrocarbon formation in the form of soot in the oven. Therefore, the burner flame generating ports are designed to a relatively small diameter; and, this results in a relatively high velocity of the fuel gas-air mixture discharging from the port. The relatively high velocity of the mixture discharging from the port makes it quite difficult to place a spark ignitor in the proper location for igniting flame as the mixture initially discharges from the port upon opening of the burner flow control valve.

Thus it has long been desired to provide a way or means of improving the initiation of flame at a burner discharge port utilizing a spark discharge type ignitor and to provide such improvement without increasing the manufacturing cost of the ignitor components.

It is an object of the present invention to provide an improved spark discharge type ignitor for igniting a fuel gas-air mixture discharging from a burner port.

It is a further object of the present invention to provide a spark discharge type ignitor system for igniting fuel gas flowing from a burner port and to provide such a system having multiple sparking electrode surfaces which are equidistant from the high voltage potential electrode. It is a further object of the present invention to provide flame presence sensing by current rectification in the presence of flame.

The present invention provides a plenum area adjacent the burner discharge port and an electrode is disposed in the plenum area for providing spark discharge thereto for igniting the fuel gas-air mixture discharging from the burner port. In the preferred embodiment, the plenum is formed as a cut-out or aperture in a plenum member attached to the burner; and, the periphery of the plenum aperture provides multiple points for spark discharge which are equidistant from an electrode centrally disposed with respect to the aperture. In one embodiment the aperture formed at generally right angles to the direction of flow from the burner port. In another embodiment the plenum aperture is disposed in a plate generally parallel to the burner flame generating port surface. A portion the flow from the burner port is trapped in the plenum aperture and the velocity is reduced such that upon spark discharge the fuel gas-air mixture is readily ionized and ignited by the spark discharge.

Upon ignition, the plenum aperture surrounding the electrode tip tends to direct and hold flame about the electrode and enhances flame rectification for flame presence sensing.

FIG. 1 illustrates in axonometric projection a portion of a fuel burner tube with the plenum aperture disposed at right angles to the flow from flame generating ports;

FIG. 2 is a front side elevation view of another preferred embodiment of the invention having the plenum aperture in a plate parallel to the flame generating port surface;

FIG. 3 is an enlarged view of the encircled portion of FIG. 2;

FIG. 4 is a top or plan view of the right end portion of FIG. 2; and,

FIG. 5 is a section view taken along section indicating lines 5--5 of FIG. 3.

Referring to FIG. 1, one embodiment of the ignitor system is indicated generally at 10 and includes a burner tube 12, such as an oven burner, which has the hollow interior thereof formed to receive a supply of gaseous fuel-air mixture from a source (not shown) which enters the burner tube 12 from the direction indicated by the black arrow. A plurality of flame generating ports indicated by reference numerals 14, 16, 18 are provided in spaced generally aligned relationship along one sidewall of the burner tube 12, which in the illustrated embodiment has a generally rectangular or square cross-section. It will be understood however that the burner port may have any suitable configuration such as, for example, a circular or oval cross-section. The burner tube in the illustrated embodiment has a seamless configuration but may also be fabricated by joining together half shells as, for example, by weldment.

A plenum forming member in the form of plate 20 has one side thereof attached to the wall 22 of the burner and is disposed in closely spaced proximity to the burner port 18. The plenum forming plate 20 has a plenum cut-out 24 formed therein which has a slot 26 formed in one side thereof, which slot 26 extends to the burner wall 22 such that a portion of the gaseous fuel-air mixture emanating or flowing from port 18 travels along the slot into the plenum area 24. In the present practice of the invention, the cut-out 24 has a generally circular configuration; and, the plate 20 is welded to the wall 22 of the burner tube such that the plate extends therefrom in a generally right angle configuration. This arrangement serves to trap and reduce the velocity of at least a portion of the fuel-air mixture flowing from flame generating port 18.

An electrode 28 is disposed adjacent the cut-out 24 and preferably has the end 30 thereof disposed centrally within the circular cut-out 24 such that the periphery of the cut-out is equidistant from the end 30 of the electrode. The distal or remote end of the electrode denoted by reference numeral 32 is connected to a source of relative high voltage electrical potential with respect to the plate 20, which in the present practice of the invention is grounded.

It will be understood that upon initiation of the flow of gaseous fuel-air mixture into the hollow of burner 12, the mixture flows at an increased velocity through the ports 14, 16, 18, with the flow from port 18 entering the slot 26 and circular aperture 24 where the velocity is reduced. Upon the oven user actuating a control (not shown) a high voltage (+v) is applied to electrode 28 and an arc or spark discharge from the end 30 of the electrode to the periphery of the cut-out 24 and ignition occurs and flame is generated at the port 18. It will be understood that the plate 20 may be located intermediate the ports 16 and 18 such that flame will be initiated practically simultaneously at ports 16 and 18.

Referring to FIGS. 2 through 5, another embodiment of the system is illustrated generally at 40 and includes a burner tube 42 having a plurality of flame generating ports 44 provided thereon and an inlet air aspirator indicated generally at 46 which is provided on an end 48 of the tube formed at right angles to the tube 42.

A burner support mounting member indicated generally at 50 has a portion thereof indicated by reference numeral 52 configured to conform to the outer surface of tube 42 and is attached thereto by any suitable expedient, as for example, weldment. The burner mounting support member 50 includes a flange 54 for mounting the burner tube to the interior of the oven.

An ignitor support bracket 54 is attached to the support member 50 by any suitable expedient such, as for example, weldment or riveting of a flange portion 56 welded to a plate 58 which comprises a portion of the burner tube support member 50. A portion of the ignitor bracket 54 distal the flange 56 is formed to a generally circular configuration as denoted by reference numeral 57 and has received therein an ignitor probe 60 which is securely clamped therein and maintained in a predetermined position.

The ignitor probe 60 has an electrode 62 extending from the end thereof which electrode is formed in a generally right angle bend to have an end 64 thereof disposed, preferably centrally, within an aperture 66 formed in the plate 58 which is disposed and located such that aperture 66 is positioned over at least one of the burner flame generating ports 44 and is spaced therefrom a predetermined distance by a flange 68 formed on plate 58.

Thus, upon opening of a fuel valve (not shown) fuel enters aspirator 46 and a mixture of gaseous fuel and air flows in tube 42 and discharges from the ports 44 and a portion thereof is contained in the region of the cut-out 66. Upon spark discharge of the ignitor end 64 to multiple points about the periphery of circular cut-out or aperture 66, the mixture is ignited and flame is retained in the aperture 66. The flame retained in the aperture 66 is utilized to rectify a current flowing from electrode end 64 to aperture 66, which rectification may be sensed by suitable circuitry (not shown) in a manner well known in the art and thus the ignitor arrangement provides an inherent flame sensing ability to the ignition system of the present invention. It will be understood that although a circular configuration for aperture 66 is preferred to provide an enlarged spark discharge area equidistant from the electrode end 64, that other configurations for the aperture 66 may be employed as, for example, oval, elliptical, elongated slot or an open U-shaped cut-out.

The present invention thus provides an improved spark discharge type ignition system for igniting fuel gas-air mixture flowing from burner ports and has particular applicability to burner tubes of the type employed for household cooking ovens.

The present invention provides for multiple discharging of the sparking to a plurality of surface points by placement of the spark electrode in an aperture or cut-out which serves to retain flame when the fuel-air mixture from the flame generating port is ignited. The flame retained in the cut-out or aperture is then utilized to rectify a flow of sensing current which rectification is sensed to give proof of flame presence.

Although the present invention has hereinabove been described with respect to the illustrated embodiments, it will be understood that the invention is capable of modification and variation and is limited only by the following claims.